Coatings are applied to commercial seeds for a number of reasons, including binding of pesticides, retardation of germination and for the controlled release of fertilizers, plant hormones, pesticides, etc. The coatings currently used are usually water soluble or water degradable polymers. However, most of these coatings have the weakness that they are not permeable to gases and that they have a low ability to control rate of release of materials contained within them. Seed coatings generally must protect the seed mechanically but be capable of transmission of moisture, visible light, oxygen, carbon dioxide and certain other materials.
Magimel-Pelonnier et al., in U.S. Pat. No. 2,923,095, issued Feb. 2, 1960, utilized organosilicic derivatives for modifying or controlling the degree of hydration of, and transpiration of water from, vegetable material of the nature of growing plants, plants removed from the ground, cuttings of plants, seeds and the like. However Magimel-Pelonnier et al. does not teach the use of crosslinked silicone polymers for the protection of the seeds or the incorporation of additives.
Several patents issued to Young et al. teach the use of organopolysiloxanes possessing hydroxyl groups or groups hydrolyzable to hydroxyl groups for the controlled release of pesticides e.g., insecticides. See U.S. Pat. Nos. 4,282,207, issued Aug. 4, 1981; 4,212,897, issued July 15, 1980; 4,205,096, issued May 27, 1980; 4,200,664, issued Apr. 29, 1980; 4,198,441, issued Apr. 15, 1980; 4,172,904, issued Oct. 30, 1979; and 4,283,387, issued Aug. 11, 1981. However, the compositions of the Young et al. patents are prepared in organic solvents and unlike the compositions of the instant invention, cannot be prepared in water because the starting materials would rapidly and uncontrollably hydrolyze without building up an elastomeric polymer. Furthermore, the Young et al. patents do not teach the crosslinking of the polyorganosiloxanes utilized in the coating methods of the instant invention. Finally, the Young et al. patents do not teach the coating of seeds, seedlings, meristematic tissue, or plant embryos.
German patent DE No. 3150631, issued July 21, 1983 to Weber et al., relates to seed dressing with a phytotoxic pesticide incorporated into a slow-release composition. Weber et al. teaches the possible use of a silicone in the composition but requires an additional organic or inorganic binder such as methyl cellulose, polyvinyl acetate, a polyacrylate, a ureaformaldehyde resin, perlite, or vermiculite. Such additional binders are not necessary in the crosslinked silicone seed coatings of the instant invention. Weber et al. does not teach the use of crosslinked silicone polymers as the binder.
In U.S. Pat. No. 3,156,550, issued Nov. 10, 1964, to Bartels, there is taught the use of two adherent layers applied to seeds for protection. However no use of polydimethylsiloxane polymers is indicated.
U.S. Pat. No. 4,370,160, issued Jan. 25, 1983, to Ziemelis, teaches that a broad range of materials can be entrapped in cured microcapsules or microparticles of polydimethylsiloxane. While Ziemelis mentions insecticides as one of the possible materials which may be encapsulated within curable polydimethylsiloxane, no mention is made therein of seeds, seedlings, meristematic tissue or plant embryos
Redenbaugh, in U.S. Pat. No. 4,562,663, issued Jan. 7, 1986, and in U.S. Pat. No. 4,583,320, issued Apr. 22, 1986, describes the use of various materials to encapsulate meristematic tissue, plant embryos, and seeds, Silicones are not mentioned.
There is a need for artificial seeds in which plant embryos, nutrients, plant hormones, and fertilizers are encapsulated, free of disease, in a coating able to provide sufficient sunlight and water vapor transmission to facilitate germination. In sugar cane, for example, there are ordinarily microorganisms present in the plants and they consume some of the plant's nutrients, reducing the amount of sucrose produced by the cane. Therefore, sugar cane growers grow a callus of cane cells in the presence of antibiotics. The cane that results when the callus cells are caused to differentiate is then free of microorganisms. However it has not been possible to make an artificial seed from these plant embryos. Rather, the embryos are propagated in a greenhouse atmosphere until fully developed cane is produced. The stalks are then cut and planted in a field. When the crop is mature, the cane stalks are cut and taken to the customer's fields and planted in rows. This process is labor intensive and suffers from the fact that cane, once cut, is subject to rapid deterioration due to desiccation and attack by airborne microorganisms.
Thus, an object of this invention is to provide a technique whereby cultivated plant tissue or seeds or seedlings or plant embryos may be insulated from harmful conditions.